WASHINGTON (Reuters) - U.S. Army Sergeant Bowe Bergdahl suffered harsh treatment at the hands of his Taliban captors, including long periods of solitary confinement, according to U.S. military officials who also said the soldier was struggling emotionally and had not yet called his parents.

Bergdahl, released in Afghanistan on May 31 in exchange for five Taliban detainees from the Guantanamo Bay prison, is being treated at the U.S. Army hospital in Landstuhl, Germany.

A national controversy has erupted over whether President Barack Obama paid too high a price for Bergdahl's freedom. [ID:nL1N0ON292]. But U.S. Secretary of State John Kerry fiercely defended the exchange.

"It would have been offensive and incomprehensible to consciously leave an American behind. No matter what," Kerry, a Vietnam War veteran, told CNN.

One U.S. military official told Reuters the 28-year-old was physically well enough to travel back to the United States for treatment. He is suffering from disorders affecting his skin and gums that could be expected after his five-year captivity, the official said, confirming a report in the New York Times.

The newspaper reported on Sunday that Bergdahl told medical officials in Germany the Taliban kept him in a metal cage in the dark for weeks after he tried to escape.

Bergdahl, who was a private when he was captured, does not like being called a sergeant, the rank he was promoted to while in captivity, the military official told Reuters. The soldier is struggling with emotional issues and has not contacted his parents, although he is free to do so at any time, the official told Reuters on condition of anonymity.

Another U.S. official said some of the experiences Bergdahl was relating included "harsh treatment" by the Taliban, but that was not surprising. "These are not nice people," the official told Reuters.

Pentagon spokesman Rear Admiral John Kirby declined comment on what Bergdahl was saying privately at the hospital."The Department of Defense does not comment on discussions that Sergeant Bergdahl is having with the professionals who are providing him medical and reintegration care," Kirby said in a statement. "We will respect that process in all regards. "The exchange deal with the Taliban, which was brokered by Qatar, has provoked an angry backlash in Congress over the Obama administration's failure to notify lawmakers in advance that Taliban prisoners were leaving the Guantanamo prison camp. The former inmates were sent to Qatar, where they will remain for at least a year with restrictions.

U.S. Representative Mike Rogers said on Sunday he thought at least three of the five former prisoners would return to the battlefield after they leave Qatar.

"I am absolutely convinced of that," Rogers, the Republican chairman of the House of Representatives Intelligence Committee, said on ABC's "This Week".

But Kerry made clear that they would do so at their own considerable risk.

"I'm not telling you they don't have some ability at some point to go back and get involved," Kerry said in an interview with CNN's "State of the Union" program. "But they also have the ability to get killed doing that." [ID:nL2N0OP03B]

Kerry said the United States had proven its ability to target al Qaeda fighters in Pakistan and Afghanistan and said Qatari officials would closely monitor the released Taliban.

"They're not the only ones keeping an eye on them," he said.

CIRCUMSTANCES UNCLEAR

The swap also drew criticism from some of Bergdahl's former comrades, who have charged he was captured by the Taliban in 2009 after deserting his post.

U.S. military leaders have said the circumstances of Bergdahl’s capture are unclear. Defense Secretary Chuck Hagel has urged critics to wait for all the facts to be known before rushing to judgment on Bergdahl.

The Pentagon cautioned that the Army's investigation into Bergdahl's 2009 disappearance, once it began, needed "to be respected," signaling the public may need to wait a long time for the release of the official U.S. account of what happened to him.

Obama has remained unapologetic about the deal to secure Bergdahl's release. As U.S. commander in chief, he was "responsible for those kids" and ensuring no one was left behind, he said on Thursday in Brussels.

U.S. officials said they needed to move quickly on the prisoner exchange because of concerns about Bergdahl's health as well as fears that leaks could cause the deal to collapse or prompt a Taliban member who disagreed with it to kill Bergdahl.

The U.S. House Armed Services Committee planned to hold a hearing on the release of the five Taliban prisoners on Wednesday, with Hagel due to testify.

The New York Times said the 5-foot-9 (1.72-metre) tall Bergdahl weighed 160 pounds (72 kg) and showed few signs of malnourishment or physical frailty.

The newspaper also said Bergdahl did not have access to media reports at the hospital in Germany. He is expected to be moved to a military hospital in San Antonio, although officials have given no date yet for that transfer.

Bergdahl's father, Bob Bergdahl, has received emailed death threats, an Idaho police chief said on Saturday. [ID:nL1N0OP018]

The first was received on Wednesday, the same day the city canceled a planned rally celebrating Bergdahl's release, Hailey Police Chief Jeff Gunter said. Hailey, a tourist community of 8,000 people in the mountains of central Idaho, has been buffeted by hundreds of vitriolic phone calls and emails.